1. Field of the Invention
The present invention relates to a motor driving apparatus that uses a power storage device in order to reduce the capacity of a power supply system.
2. Description of the Related Art
In a motor driving apparatus for driving a machine tool, industrial machine, robot, or the like, a PWM converter which can control DC link voltage to a desired voltage higher than the peak value of the input voltage, at near unity power factor through PWM switching operation of power semiconductor devices, is widely used as a converter for converting the input AC power to DC power.
Japanese Unexamined Patent Publication No. 2000-236679 discloses a technique in which a power storage device is connected to the output of a PWM converter and the PWM converter is operated so as to limit the input current, with provisions made to use the power storage device as a buffer to provide motor driving power, thereby suppressing peaks in the power supplied from the power supply during motor acceleration and also suppressing peaks in the regenerative power flowing back to the power supply during motor deceleration.
According to this technique, the power peaks are suppressed by the buffering capability of the power storage device. However, since control is performed so that the voltage of the power storage device is maintained constant at all times, the regenerative power that occurs during motor deceleration is returned to the power supply or, if this is not possible, the regenerative power ends up being consumed by resistors and is not stored in the power storage device for reuse. Accordingly, with this technique, the total amount of power that has to be supplied from the power supply during motor acceleration and constant speed operation does not become smaller than when the power storage device was not used. There is therefore the problem that the above technique does not contribute to significantly easing the requirements on the power supply capacity.